Transformer core structure



Dec. 27,1938. 0. EPPELSHEIPYJIER 2,142,066

; TRANSFORMER CORE STRUCTURE Filed Dec. 2, 195'? INVENTOR. flA/v/EL .EPPEL-SHE/MEA.

'BY WQPM ATTORNEYS.

Patented 27, 19 38 2,142,068 muss-0am cons s'raocroan Daniel Eppellhe er, minim, om Application Deoember 2, 1931, Serial No. 1mm '1 claims. (01. 450

My invention relates a class known as reactors,

electrical apparatus of and more particularly to electrical transformers and core structures therefor. Cores for electrical transformers are generally composed of a large number of laminae which have been sheared and punched from sheet material, which may be of a high grade of silicon steel, although alloys having tics and containing similar characterisnickel and cobalt have also been used. Such laminations are built up to form the transformer cores, and the individual laminae are generally insulated from each other in order to reduce eddy current losses.

There are certain tions among which are shaped laminae from considerable scrap loss; high magnetic properties pensive, the cost of ably increased. Furthermore, working of the metal. forming objections tosuch constructhat the punching of odd sheet material involves a and since the material of is usually relatively exthe transformer is consider it is blown. that a the cores has a deleterious effect upon the magnetic properties thereof, so that in accordance with present practice the laminae after they are sheet material have to be anpunched from the sheared and nealed or heat treated in one way or another to eliminate these Another objection the labor cost is high deleterious effects.

to this construction is that because of the large number of pieces which have to be assembled to constitute a single core.

the, order of several This number may be of thousand. Furthermore, in

the assembly of the core pieces care must be taken that the and the joints must laminae are properly superposed be arranged in such a way that the magnetic circuit is not seriously affected.

gnetic reluctance due to the joints in the magnetic circuit is generally such that considerably more magnetic core material must be provided in the design of such transformers in order that they will perform according to the specifications of dimculties and objections in With the above the users.

mind, it is an object of my invention toprovlde a novel core structure for reactors and more particularly for electrical transformers which will be free, at least to a great extent, of the objections above noted.

It is an object of my invention to provide a core structure in which the laminae are continuous, and in which the direction of the magnetic path coincides with the direction of rolling of the material constituting the core. It is a further object of my invention to provide a core structure of what is known as the three-leg type,

vide a core structure of which is nevertheless composed of only two pieces so that a great simplicity of manufacture is achieved. It is a still further object of my inven-. tion to cut down the amount of shearing and punching to an absolute minimum, so that the 5 electrical properties. will not be deleteriously affected.

These and other objects which will be set forth hereinafter or will be apparent to one skilled in the art upon reading this specification, I accomplish by that certain construction and arrangement of parts of which I shall now describe a preferred embodiment. Reference is now. made to the drawing which forms a part hereof, and in which: 1

Figure 1 is an elevational view of .a transformer according to my invention.

Fig. 2 is a plan view of the same.

Fig. 3 is a horizontal cross sectional view of the center leg member. 20 Fig. 4 is a view similar to Fig. 1 showing a diiferent form of loop.

Fig. 5 is a view similar other form of loop.

Fig. 6 is a view to Fig. 4 showing ansimilar to-Fig. 3 showing a different form of center leg.,

Fig. '1 is a view similar to Fig. 3 showing another form of center leg.

Briefly, in the practice of my invention, I prothe three-leg type in which the two outer legs and the yokes are formed from a strip of sheet material wound upon itself to form a loop as indicated at 8 in Fig. 1. The member 8, of course, may be formed from more than a single strip; for example, it might be formed by winding two or more strips into a loop or by winding a plurality of strips welded end-toend into a loop. The strips forming the member 8 when made of materials having marked directional properties are taken with their length parallel to the ails of rolling of the original sheet from which they have been sheared, or that of greatest permeability if it differs from the direction of rolling. so that in the finished transformer the magnetic path will be coincident with the direction which results in the most effective use of the material. The shearing of the strip material to form the member 8 will not ordinarily affect its properties very much; but any effects so produced may be removed by an- 50 nealing after slitting. The member 8 may of course be annealed after complete fabrication, and the whole ferrous part of the transformer may be annealed to remove strains caused in shearim. coiling or the like.

Although I have shown in Figs. 1 and 2 a circular member I, it will be understood that depending upon the shape of the bobbin upon which the strip is wound, the member I could be oval or elliptical, as shown in Fig. 4, or rectangular, with rounded corners, as shown in Fig. 5, or indeed of any desired shape. In the winding of the strip an appropriate tension may be maintained in any desired way; and the strip is prevented from unwinding by means of one or more tension bands 8a.

The center leg, indicated in the drawing at 9,

.I prefer to form by spirally winding a sheet of magnetic material into a roll form. If the center leg is so formed it may be rolled so that the axis of the roll will correspond to the direction of rolling of the sheet. I prefer to roll the center leg 9 in such a way as to leave a central bore la for purposes which will be described hereinafter.

For assembling the two parts together I provide for forming a taper on each end of the member 9, and I provide a tapered recess in themember I adapted to make a perfect seat for the tapered portion of the leg 9. The two parts may readily be assembled .by compressing the loop 8 to increase its diameter on the axis of the recesses l0, and the member 9 may then be simply slipped into place and will be held in position by the natural resiliency of the loop I in returning to its original form. In the embodiment of Fig. 3, if desired, the center leg may be of such length that a bolt and nut (I I, I!) may be used to contract the loop 8 on its long axis until it is circular. If the tapered recesses II are provided with holes extending completely through the member I, the center leg may be cooled by fluid passing through the bore So. If it is desired to make a tighter fit by adding pressure to the Joints between the member 9 and the member 8, a non-magnetic bolt Il may be passed through the bore 9a and held in place by means of a nut II. If it is still desired to provide for extra cooling the bolt I I may, of course, be hollow.

In completing the transformer, the low voltage coils are wound onto the member 9, as indicated at H, and the high voltage windings are wound over the low voltage windings, as indicated at i 3, or in any manner which the results desired would indicate to be preferable.

It will thus be seen that I have provided a relatively simple core structure of the three-leg type in which the magnetic path is continuous and uninterrupted throughout the outer legs and yokes. It will be seen that I have provided an excellent magnetic joint between the yokes and the center leg and that I have provided for cooling if that is deemed necessary or advisablej Furthermore, it will be noted that I have provided a transformer in which the magnetic path is always in the direction of rolling of the material constituting the core or the direction of greatest permeability thereof, and that I have reduced the working of the metal to an absolute minimum whereby the magnetic properties of the material are not adversely eilected.

It will be understood that the particular circular form of the member 8 shown in the drawing is not to be considered as constituting a limitation upon my invention, and that other shapes may be used, provided the material is formed in accordance with the spirit of this invention. Although I have shown as a preferred embodiment in Fig. 3, a center leg formed from a sheet of material spirally wound, it will be understood that the same purpose would be served by center leg formed simply from row, flat strips sheared so that their length inthedirection.asshowninl"ig.d,in permeability would be highest at the operating induction, or by more than one leg, the surrounded by the primary and secondary windings, as shown in Fig. '7. It will, of course. be clear that in the embodiment shown, the amount of shearing necessary is greatly reduced.

The laminae may be insulated in any conventional or desired way either prior to or during winding; but the particular manner of the core laminae has not been described because it forms no part of my invention.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent, is:

l. A core structure for a transformer comprising magnetic material wound to form a laminated loop-shaped member constituting a magnetic yoke, and a center leg member bridging the yoke,

'said leg being of laminated construction, and

magnetic connections between the ends of said leg and said yoke, said leg being tapered at its ends substantially to a point, the yoke member having at its opposite sides correspondingly shaped recesses to receive the ends of the leg, the said leg being less in its cross-sectional dimension than the width of the inner lamina of the yoke, whereby the inner lamina of the yoke remains unsevered by the recesses therein, the recesses in successive laminae outwardly being of less and less area, whereby the yoke remains a strong unitary structure which may be sprung to receive the ends of the leg, the relationship of the laminae in the leg and the laminae in the yoke being a substantially continuous one, lamina for lamina, so that lines of magnetic force traversing the leg and yoke traverse paths longitudinally of all laminae without cutting across laminae.

2. A structure as claimed in claim 1 in which the direction of magnetic lines of force in all laminae coincides with the direction of rolling of said laminae.

3. A structure as claimed in claim 1, in which.

the yoke is formed of a single strip of magnetic material having a high permeability longitudinally of the strip and a relatively lower permeability in other directions- 7 4.Astructureasclaimedinclaimlinwhich said leg is formed of magnetic material wound upon itself spirally, in which the ends of the leg are tapered to a conical formation, and in which the yoke has corresponding conical recesses.

5. A structure as claimed in claim 1 in which said leg is formed of magnetic material wound upon itself spirally, in which the ends of the leg are tapered to a conical formation, and in which the yoke has corresponding conical recesses, the central portion of said leg being hollow, and a bolt passing through said yoke and said leg to hold said parts in assembled relationship.

6. A structure as claimed in claim 1 in which said leg is formed of magnetic material wound upon itself spirally, in which the ends of the leg are tapered to a conical formation, and in which the yoke has corresponding conical recesses, said yoke being formed of a single strip of silicon steel having a high permeability in the direction of its length and a relatively lower permeability in other directions, and said leg being formed of similar material in which the direcoi its length and a relatively lower permeability in other directions, and said leg being formed of similar material in which the direction of greatest permeability coincides with the direction of the axis of said leg, and fastening means passing through said yoke and said leg to hold said parts in assembled relationship.

DANIEL EPPELS. 

